Experimental Search for $n \rightarrow n'$ Oscillations to Explain the Neutron Lifetime Discrepancy

The theory of "mirror matter" restores parity to the standard model by hypothesizing a copy of the standard model with right-handed weak interactions. One potential way to explain the $>4 \sigma$ discrepancy between beam and bottle neutron lifetime experiments invokes neutrons oscillating into their mirror neutron partners. Mirror neutron oscillations as a source of loss in bottle lifetime experiments are constrained by the agreement between $V_{ud}$ extracted from neutron $\beta$-decay and the value of $V_{ud}$ required for CKM unitarity. However, in the event of a small mass difference $\Delta m$ between the normal and mirror neutron states, the 4.6 T magnetic field present in the NIST Beam Lifetime experiment could cause an apparent increase in the measured $\tau_n$. An experiment at Oak Ridge National Lab probed this theory by searching for the hypothesized reappearance of neutrons passing through a B$_4$C absorber inside a magnetic field varying between a peak strength of -6.6 T and +6.6 T. This talk presents new limits on neutron oscillations into non-degenerate mirror matter, excluding this effect as an explanation of the neutron lifetime discrepancy. We will also discuss further efforts to improve these limits and search for other models of $n \rightarrow n'$ oscillation.